1K32

Crystal structure of the tricorn protease

External Resource: Annotation

Domain Annotation: SCOP/SCOPe Classification
Domain Annotation: SCOP2 Classification
Domain Annotation: ECOD Classification
Domain Annotation: CATH
Protein Family Annotation
Gene Ontology: Gene Product Annotation
InterPro: Protein Family Classification
Structure Motif: Primary M-CSA Annotation

Domain Annotation: SCOP/SCOPe Classification SCOP-e Database Homepage

Chains	Domain Info	Class	Fold	Superfamily	Family	Domain	Species	Provenance Source (Version)
A	d1k32a1	All beta proteins	PDZ domain-like	PDZ domain-like	Tail specific protease PDZ domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
A	d1k32a2	All beta proteins	6-bladed beta-propeller	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
A	d1k32a3	All beta proteins	7-bladed beta-propeller	Tricorn protease domain 2	Tricorn protease domain 2	Tricorn protease domain 2	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
A	d1k32a4	Alpha and beta proteins (a/b)	ClpP/crotonase	ClpP/crotonase	Tail specific protease, catalytic domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
B	d1k32b1	All beta proteins	PDZ domain-like	PDZ domain-like	Tail specific protease PDZ domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
B	d1k32b2	All beta proteins	6-bladed beta-propeller	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
B	d1k32b3	All beta proteins	7-bladed beta-propeller	Tricorn protease domain 2	Tricorn protease domain 2	Tricorn protease domain 2	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
B	d1k32b4	Alpha and beta proteins (a/b)	ClpP/crotonase	ClpP/crotonase	Tail specific protease, catalytic domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
C	d1k32c1	All beta proteins	PDZ domain-like	PDZ domain-like	Tail specific protease PDZ domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
C	d1k32c2	All beta proteins	6-bladed beta-propeller	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
C	d1k32c3	All beta proteins	7-bladed beta-propeller	Tricorn protease domain 2	Tricorn protease domain 2	Tricorn protease domain 2	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
C	d1k32c4	Alpha and beta proteins (a/b)	ClpP/crotonase	ClpP/crotonase	Tail specific protease, catalytic domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
E	d1k32e1	All beta proteins	PDZ domain-like	PDZ domain-like	Tail specific protease PDZ domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
E	d1k32e2	All beta proteins	6-bladed beta-propeller	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
E	d1k32e3	All beta proteins	7-bladed beta-propeller	Tricorn protease domain 2	Tricorn protease domain 2	Tricorn protease domain 2	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
E	d1k32e4	Alpha and beta proteins (a/b)	ClpP/crotonase	ClpP/crotonase	Tail specific protease, catalytic domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
F	d1k32f1	All beta proteins	PDZ domain-like	PDZ domain-like	Tail specific protease PDZ domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
F	d1k32f2	All beta proteins	6-bladed beta-propeller	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
F	d1k32f3	All beta proteins	7-bladed beta-propeller	Tricorn protease domain 2	Tricorn protease domain 2	Tricorn protease domain 2	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
F	d1k32f4	Alpha and beta proteins (a/b)	ClpP/crotonase	ClpP/crotonase	Tail specific protease, catalytic domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
D	d1k32d1	All beta proteins	PDZ domain-like	PDZ domain-like	Tail specific protease PDZ domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
D	d1k32d2	All beta proteins	6-bladed beta-propeller	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	Tricorn protease N-terminal domain	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
D	d1k32d3	All beta proteins	7-bladed beta-propeller	Tricorn protease domain 2	Tricorn protease domain 2	Tricorn protease domain 2	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)
D	d1k32d4	Alpha and beta proteins (a/b)	ClpP/crotonase	ClpP/crotonase	Tail specific protease, catalytic domain	Tricorn protease	(Thermoplasma acidophilum ) [TaxId: 2303 ],	SCOPe (2.08)

Domain Annotation: SCOP2 Classification SCOP2 Database Homepage

Chains	Type	Family Name	Domain Identifier	Family Identifier	Provenance Source (Version)
A	SCOP2 Family	Tail specific protease catalytic domain	8025390	4003564	SCOP2 (2022-06-29)
A	SCOP2 Family	Tricorn protease N-terminal domain	8025388	4003126	SCOP2 (2022-06-29)
A	SCOP2 Family	Tricorn protease domain 2	8025389	4003140	SCOP2 (2022-06-29)
A	SCOP2 Family	Tail specific protease PDZ domain	8025387	4002827	SCOP2 (2022-06-29)
A	SCOP2 Superfamily	ClpP/crotonase	8037769	3000033	SCOP2 (2022-06-29)
A	SCOP2 Superfamily	Tricorn protease N-terminal domain	8037767	3000291	SCOP2 (2022-06-29)
A	SCOP2 Superfamily	Tricorn protease domain 2	8037768	3000315	SCOP2 (2022-06-29)
A	SCOP2 Superfamily	PDZ domain-like	8037766	3000388	SCOP2 (2022-06-29)
B	SCOP2B Superfamily	PDZ domain-like	8037766	3000388	SCOP2B (2022-06-29)
B	SCOP2B Superfamily	Tricorn protease domain 2	8037768	3000315	SCOP2B (2022-06-29)
B	SCOP2B Superfamily	ClpP/crotonase	8037769	3000033	SCOP2B (2022-06-29)
B	SCOP2B Superfamily	ClpP/crotonase	8037769	3000033	SCOP2B (2022-06-29)
B	SCOP2B Superfamily	Tricorn protease N-terminal domain	8037767	3000291	SCOP2B (2022-06-29)
C	SCOP2B Superfamily	ClpP/crotonase	8037769	3000033	SCOP2B (2022-06-29)
C	SCOP2B Superfamily	Tricorn protease domain 2	8037768	3000315	SCOP2B (2022-06-29)
C	SCOP2B Superfamily	Tricorn protease N-terminal domain	8037767	3000291	SCOP2B (2022-06-29)
C	SCOP2B Superfamily	ClpP/crotonase	8037769	3000033	SCOP2B (2022-06-29)
C	SCOP2B Superfamily	PDZ domain-like	8037766	3000388	SCOP2B (2022-06-29)
E	SCOP2B Superfamily	ClpP/crotonase	8037769	3000033	SCOP2B (2022-06-29)
E	SCOP2B Superfamily	Tricorn protease N-terminal domain	8037767	3000291	SCOP2B (2022-06-29)
E	SCOP2B Superfamily	Tricorn protease domain 2	8037768	3000315	SCOP2B (2022-06-29)
E	SCOP2B Superfamily	PDZ domain-like	8037766	3000388	SCOP2B (2022-06-29)
E	SCOP2B Superfamily	ClpP/crotonase	8037769	3000033	SCOP2B (2022-06-29)
F	SCOP2B Superfamily	Tricorn protease domain 2	8037768	3000315	SCOP2B (2022-06-29)
F	SCOP2B Superfamily	Tricorn protease N-terminal domain	8037767	3000291	SCOP2B (2022-06-29)
F	SCOP2B Superfamily	ClpP/crotonase	8037769	3000033	SCOP2B (2022-06-29)
F	SCOP2B Superfamily	ClpP/crotonase	8037769	3000033	SCOP2B (2022-06-29)
F	SCOP2B Superfamily	PDZ domain-like	8037766	3000388	SCOP2B (2022-06-29)
D	SCOP2B Superfamily	Tricorn protease N-terminal domain	8037767	3000291	SCOP2B (2022-06-29)
D	SCOP2B Superfamily	PDZ domain-like	8037766	3000388	SCOP2B (2022-06-29)
D	SCOP2B Superfamily	ClpP/crotonase	8037769	3000033	SCOP2B (2022-06-29)
D	SCOP2B Superfamily	Tricorn protease domain 2	8037768	3000315	SCOP2B (2022-06-29)
D	SCOP2B Superfamily	ClpP/crotonase	8037769	3000033	SCOP2B (2022-06-29)

Domain Annotation: ECOD Classification ECOD Database Homepage

Chains	Family Name	Domain Identifier	Architecture	Possible Homology	Homology	Topology	Family	Provenance Source (Version)
A	PF14685	e1k32A1	A: beta barrels	X: PDZ domain (From Topology)	H: PDZ domain (From Topology)	T: PDZ domain	F: PF14685	ECOD (1.6)
A	F_UNCLASSIFIED	e1k32A2	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 6-bladed	F: F_UNCLASSIFIED	ECOD (1.6)
A	PF07676	e1k32A3	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 7-bladed	F: PF07676	ECOD (1.6)
A	PF14684	e1k32A5	A: alpha bundles	X: Tail specific protease helical domain (From Topology)	H: Tail specific protease helical domain (From Topology)	T: Tail specific protease helical domain	F: PF14684	ECOD (1.6)
A	PF03572	e1k32A6	A: a/b three-layered sandwiches	X: ClpP/crotonase (From Topology)	H: ClpP/crotonase (From Topology)	T: ClpP/crotonase	F: PF03572	ECOD (1.6)
B	PF14685	e1k32B4	A: beta barrels	X: PDZ domain (From Topology)	H: PDZ domain (From Topology)	T: PDZ domain	F: PF14685	ECOD (1.6)
B	F_UNCLASSIFIED	e1k32B2	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 6-bladed	F: F_UNCLASSIFIED	ECOD (1.6)
B	PF07676	e1k32B5	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 7-bladed	F: PF07676	ECOD (1.6)
B	PF14684	e1k32B3	A: alpha bundles	X: Tail specific protease helical domain (From Topology)	H: Tail specific protease helical domain (From Topology)	T: Tail specific protease helical domain	F: PF14684	ECOD (1.6)
B	PF03572	e1k32B1	A: a/b three-layered sandwiches	X: ClpP/crotonase (From Topology)	H: ClpP/crotonase (From Topology)	T: ClpP/crotonase	F: PF03572	ECOD (1.6)
C	PF14685	e1k32C4	A: beta barrels	X: PDZ domain (From Topology)	H: PDZ domain (From Topology)	T: PDZ domain	F: PF14685	ECOD (1.6)
C	F_UNCLASSIFIED	e1k32C2	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 6-bladed	F: F_UNCLASSIFIED	ECOD (1.6)
C	PF07676	e1k32C5	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 7-bladed	F: PF07676	ECOD (1.6)
C	PF14684	e1k32C3	A: alpha bundles	X: Tail specific protease helical domain (From Topology)	H: Tail specific protease helical domain (From Topology)	T: Tail specific protease helical domain	F: PF14684	ECOD (1.6)
C	PF03572	e1k32C1	A: a/b three-layered sandwiches	X: ClpP/crotonase (From Topology)	H: ClpP/crotonase (From Topology)	T: ClpP/crotonase	F: PF03572	ECOD (1.6)
E	PF14685	e1k32E3	A: beta barrels	X: PDZ domain (From Topology)	H: PDZ domain (From Topology)	T: PDZ domain	F: PF14685	ECOD (1.6)
E	F_UNCLASSIFIED	e1k32E1	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 6-bladed	F: F_UNCLASSIFIED	ECOD (1.6)
E	PF07676	e1k32E5	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 7-bladed	F: PF07676	ECOD (1.6)
E	PF14684	e1k32E2	A: alpha bundles	X: Tail specific protease helical domain (From Topology)	H: Tail specific protease helical domain (From Topology)	T: Tail specific protease helical domain	F: PF14684	ECOD (1.6)
E	PF03572	e1k32E4	A: a/b three-layered sandwiches	X: ClpP/crotonase (From Topology)	H: ClpP/crotonase (From Topology)	T: ClpP/crotonase	F: PF03572	ECOD (1.6)
F	PF14685	e1k32F2	A: beta barrels	X: PDZ domain (From Topology)	H: PDZ domain (From Topology)	T: PDZ domain	F: PF14685	ECOD (1.6)
F	F_UNCLASSIFIED	e1k32F1	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 6-bladed	F: F_UNCLASSIFIED	ECOD (1.6)
F	PF07676	e1k32F5	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 7-bladed	F: PF07676	ECOD (1.6)
F	PF14684	e1k32F3	A: alpha bundles	X: Tail specific protease helical domain (From Topology)	H: Tail specific protease helical domain (From Topology)	T: Tail specific protease helical domain	F: PF14684	ECOD (1.6)
F	PF03572	e1k32F4	A: a/b three-layered sandwiches	X: ClpP/crotonase (From Topology)	H: ClpP/crotonase (From Topology)	T: ClpP/crotonase	F: PF03572	ECOD (1.6)
D	PF14685	e1k32D2	A: beta barrels	X: PDZ domain (From Topology)	H: PDZ domain (From Topology)	T: PDZ domain	F: PF14685	ECOD (1.6)
D	F_UNCLASSIFIED	e1k32D5	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 6-bladed	F: F_UNCLASSIFIED	ECOD (1.6)
D	PF07676	e1k32D1	A: beta duplicates or obligate multimers	X: beta-propeller-like	H: beta-propeller	T: 7-bladed	F: PF07676	ECOD (1.6)
D	PF14684	e1k32D4	A: alpha bundles	X: Tail specific protease helical domain (From Topology)	H: Tail specific protease helical domain (From Topology)	T: Tail specific protease helical domain	F: PF14684	ECOD (1.6)
D	PF03572	e1k32D3	A: a/b three-layered sandwiches	X: ClpP/crotonase (From Topology)	H: ClpP/crotonase (From Topology)	T: ClpP/crotonase	F: PF03572	ECOD (1.6)

Domain Annotation: CATH CATH Database Homepage

Chain	Domain	Class	Architecture	Topology	Homology	Provenance Source (Version)
A	2.120.10.60	Mainly Beta	6 Propeller	Neuraminidase	Tricorn protease N-terminal domain	CATH (4.3.0)
A	2.130.10.10	Mainly Beta	7 Propeller	Methylamine Dehydrogenase	Chain H	CATH (4.3.0)
A	3.30.750.44	Alpha Beta	2-Layer Sandwich	Transcription Regulator spoIIAA		CATH (4.3.0)
A	2.30.42.10	Mainly Beta	Roll	Pdz3 Domain	PDZ domain	CATH (4.3.0)
A	3.90.226.10	Alpha Beta	Alpha-Beta Complex	2-enoyl-CoA Hydratase	Chain A, domain 1	CATH (4.3.0)
B	2.120.10.60	Mainly Beta	6 Propeller	Neuraminidase	Tricorn protease N-terminal domain	CATH (4.3.0)
B	2.130.10.10	Mainly Beta	7 Propeller	Methylamine Dehydrogenase	Chain H	CATH (4.3.0)
B	3.30.750.44	Alpha Beta	2-Layer Sandwich	Transcription Regulator spoIIAA		CATH (4.3.0)
B	2.30.42.10	Mainly Beta	Roll	Pdz3 Domain	PDZ domain	CATH (4.3.0)
B	3.90.226.10	Alpha Beta	Alpha-Beta Complex	2-enoyl-CoA Hydratase	Chain A, domain 1	CATH (4.3.0)
C	2.120.10.60	Mainly Beta	6 Propeller	Neuraminidase	Tricorn protease N-terminal domain	CATH (4.3.0)
C	2.130.10.10	Mainly Beta	7 Propeller	Methylamine Dehydrogenase	Chain H	CATH (4.3.0)
C	3.30.750.44	Alpha Beta	2-Layer Sandwich	Transcription Regulator spoIIAA		CATH (4.3.0)
C	2.30.42.10	Mainly Beta	Roll	Pdz3 Domain	PDZ domain	CATH (4.3.0)
C	3.90.226.10	Alpha Beta	Alpha-Beta Complex	2-enoyl-CoA Hydratase	Chain A, domain 1	CATH (4.3.0)
E	2.120.10.60	Mainly Beta	6 Propeller	Neuraminidase	Tricorn protease N-terminal domain	CATH (4.3.0)
E	2.130.10.10	Mainly Beta	7 Propeller	Methylamine Dehydrogenase	Chain H	CATH (4.3.0)
E	3.30.750.44	Alpha Beta	2-Layer Sandwich	Transcription Regulator spoIIAA		CATH (4.3.0)
E	2.30.42.10	Mainly Beta	Roll	Pdz3 Domain	PDZ domain	CATH (4.3.0)
E	3.90.226.10	Alpha Beta	Alpha-Beta Complex	2-enoyl-CoA Hydratase	Chain A, domain 1	CATH (4.3.0)
F	2.120.10.60	Mainly Beta	6 Propeller	Neuraminidase	Tricorn protease N-terminal domain	CATH (4.3.0)
F	2.130.10.10	Mainly Beta	7 Propeller	Methylamine Dehydrogenase	Chain H	CATH (4.3.0)
F	3.30.750.44	Alpha Beta	2-Layer Sandwich	Transcription Regulator spoIIAA		CATH (4.3.0)
F	2.30.42.10	Mainly Beta	Roll	Pdz3 Domain	PDZ domain	CATH (4.3.0)
F	3.90.226.10	Alpha Beta	Alpha-Beta Complex	2-enoyl-CoA Hydratase	Chain A, domain 1	CATH (4.3.0)
D	2.120.10.60	Mainly Beta	6 Propeller	Neuraminidase	Tricorn protease N-terminal domain	CATH (4.3.0)
D	2.130.10.10	Mainly Beta	7 Propeller	Methylamine Dehydrogenase	Chain H	CATH (4.3.0)
D	3.30.750.44	Alpha Beta	2-Layer Sandwich	Transcription Regulator spoIIAA		CATH (4.3.0)
D	2.30.42.10	Mainly Beta	Roll	Pdz3 Domain	PDZ domain	CATH (4.3.0)
D	3.90.226.10	Alpha Beta	Alpha-Beta Complex	2-enoyl-CoA Hydratase	Chain A, domain 1	CATH (4.3.0)

Protein Family Annotation Pfam Database Homepage

Chains	Accession	Name	Description	Comments	Source
A, B, C, D, E A, B, C, D, E, F	PF03572	Peptidase family S41 (Peptidase_S41)	Peptidase family S41	-	Family
A, B, C, D, E A, B, C, D, E, F	PF14684	Tricorn protease C1 domain (Tricorn_C1)	Tricorn protease C1 domain	This domain is the C1 core domain of tricorn protease. This is a mixed alpha-beta domain [1].	Domain
A, B, C, D, E A, B, C, D, E, F	PF14685	Tricorn protease PDZ domain (Tricorn_PDZ)	Tricorn protease PDZ domain	This domain is the PDZ domain of tricorn protease [1].	Domain
A, B, C, D, E A, B, C, D, E, F	PF07676	WD40-like Beta Propeller Repeat (PD40)	WD40-like Beta Propeller Repeat	-	Repeat

Gene Ontology: Gene Product Annotation Gene Ontology Database Homepage

Chains	Polymer	Molecular Function	Biological Process	Cellular Component
A, B, C, D, E A, B, C, D, E, F	tricorn protease	peptidase activity serine hydrolase activity catalytic activity, acting on a protein serine-type peptidase activity hydrolase activity catalytic activity	organic substance metabolic process organonitrogen compound metabolic process proteolysis metabolic process primary metabolic process protein metabolic process macromolecule metabolic process	intracellular anatomical structure cytoplasm cellular anatomical entity

InterPro: Protein Family Classification InterPro Database Homepage

Chains	Accession	Name	Type
A, B, C, D, E A, B, C, D, E, F	IPR005151	Tail specific protease	Domain
A, B, C, D, E A, B, C, D, E, F	IPR029045	ClpP/crotonase-like domain superfamily	Homologous Superfamily
A, B, C, D, E A, B, C, D, E, F	IPR011659	WD40-like beta propeller	Repeat
A, B, C, D, E A, B, C, D, E, F	IPR028204	Tricorn protease C1 domain	Domain
A, B, C, D, E A, B, C, D, E, F	IPR029414	Tricorn protease, PDZ domain	Domain
A, B, C, D, E A, B, C, D, E, F	IPR012393	Tricorn protease	Family
A, B, C, D, E A, B, C, D, E, F	IPR015943	WD40/YVTN repeat-like-containing domain superfamily	Homologous Superfamily
A, B, C, D, E A, B, C, D, E, F	IPR036034	PDZ superfamily	Homologous Superfamily

Structure Motif Annotation: Mechanism and Catalytic Site Atlas M-CSA Database Homepage

Chains	Enzyme Name	Description	Catalytic Residues
A	tricorn protease M-CSA #808	The tricorn protease is the core of a proteolytic system identified in the model organism Thermoplasma acidophilum. This complex functions to degrade the 7-9 residue peptides that are produced by the proteasome-mediated degradation of cellular proteins. The basic functional unit of the tricorn protease is a homohexamer of the 121 kDa subunit; however electron microscopy studies indicate that 20 copies of this 720 kDa hexamer can assemble further in vivo to form a giant 14.6 MDa icosahedral capsid.	Defined by 4 residues: HIS:A-720 [auth A-746]GLY:A-892 [auth A-918]SER:A-939 [auth A-965]ASP:A-940 [auth A-966] \| Explore in 3D: M-CSA Motif Definition Search M-CSA Motif EC: 3.4.21 (PDB Primary Data) Search M-CSA Motif + EC 3.4.21